Herbicides may injure crop plants at herbicide application rates necessary to control weed growth. Accordingly, many herbicides cannot be used for controlling weeds in the presence of certain crops. Uncontrolled weed growth, however, results in lower crop yield and reduced crop quality inasmuch as weeds compete with crops for light, water and soil nutrients. Reduction of herbicidal injury to crops without an unacceptable corresponding reduction of herbicidal action on the weeds can be accomplished by use of crop protectants known as herbicide "antidotes" or "safeners".
Many benzhydryl compounds and derivatives are known for treatment of human central nervous system diseases. For example, U.S. Pat. No. 3,544,557 to Nauta describes benzhydryl ether, acid-addition and quaternary ammonium salt compounds useful as anti-Parkinson disease agents. In particular, alkyl benzhydrylacetate compounds are shown as intermediates to obtain the Nauta '557 compounds. U.S. Pat. No. 4,003,932 to Gootjes describes diphenylmethoxyethylamine compounds as having dopaminergic properties for use in Parkinson-syndrome treatment. The Gootjes '932 compounds are mentioned as prepared from starting materials and intermediates selected from unsubstituted halo/lower-alkyl-substituted diphenylmethoxyacetamides and lower alkyl esters. In particular, the amide starting material is shown as prepared from 2-[bis(p-fluorophenyl)methoxy]acetic acid. U.S. Pat. No. 4,066,686 to Lafon describes benzhydrylsulphinyl derivatives useful for treating central nervous systems disturbances. In particular, Lafon '686 shows the following as intermediate or product compounds: benzhydrylthioacetic acid, ethyl benzhydrylthioacetate, benzhydrylsulphinylacetic acid, methyl benzhydrylsulphinylacetate, and N-[2-(benzhydrylsulphinyl)ethyl]-piperidine hydrochloride. U.S. Pat. No. 4,202,896 to Gootjes describes N-benzhydryloxyethyl-N-phenylpropylpiperazine compounds for use in Parkinson-syndrome treatment. These compounds are prepared from starting materials selected from unsubstituted or halo/lower-alkyl/lower-alkoxy-substituted diphenylmethoxyacetic/propanoic acid compounds. In particular, there is mentioned as a starting material the compound methyl diphenylmethoxyacetate.
Benzhydryl compounds and derivatives are known also for other human-related pharmaceutical purposes. For example, U.S. Pat. No. 4,205,087 to Waring describes benzhydrylacetic acid derivatives for use in anti-arthritic treatment. In particular, the compound methyl bis(4-chlorophenyl)methoxyacetate is shown. U.S. Pat. No. 4,427,590 to Allgeier et al describes triazolobenzodiazepine derivatives and oxides useful as tranquilizers and as anticonvulsant agents. An intermediate compound specifically shown is diphenylmethoxyacetic acid hydrazide. Japanese Kokai No. 74/81,379 of Kono et al shows benzhydryloxyalkylpenicillin compounds for pharmaceutical uses which are prepared from diphenylmethoxyacetic acid. A monograph by C. Van der Stelt et al [Arzneim.-Forsch., 17(11), pp. 1446-1449 (1967)], relating to guanidine and amidoxime derivatives of diphenylmethyl and tricyclic ethers, mentions the compound 2-(diphenylmethoxy)acetamide.
None of the aforementioned publications describes benzhydryl compounds for agricultural-related uses, much less for use as herbicide antidotes.
For a herbicide product to be accepted commercially, the herbicide product must provide a relatively high level of control of weeds in crops, such as rice, wheat, corn or sorghum, in addition to meeting several other criteria. For example, the herbicide must possess relatively high unit activity so that lower rates of herbicide application are feasible. Lower application rates are desirable in order to minimize exposure of the environment to the herbicide. At the same time, such herbicide must be selective in herbicidal effect so as not to injure the crops. Herbicidal selectivity can be enhanced by use of an appropriate antidote in combination with the herbicide. But identification of an antidote having high safening activity suitable for a commercially-effective herbicide is a highly complicated task. Whether a compound or class of compounds provides efficacious antidotal or safening activity is not a theoretical determination but must be done empirically. Safening activity is determined empirically by observing the complex interaction of several biological and chemical factors, namely: the type of herbicide compound; the type of weed to be controlled; the type of crop to be protected from weed competition and herbicidal injury; and the antidote compound itself. Moreover, the herbicide and antidote must each possess chemical and physical properties enabling preparation of an efficacious, stable formulation which is environmentally safe and easy to apply to the field.